1. Field of the Invention
This invention relates to a vessel cannula and, more particularly, to a cannula having varying properties, such as rigidity or resistance to deflection, along its axial length. In one aspect, the vessel cannula has one relatively rigid portion and a second portion which is more pliable than the rigid portion. This cannula is ideally suited for use in minimally invasive cardiac surgical procedures but can be adapted for use in any fluid conducting application.
2. Description of the Related Art
Vessel cannula have long been used during surgical procedures, such as cardiac surgery. The cannula are typically used to provide a fluid flow path into, out of, or through a vessel, such as a coronary artery. An example of a known cannula is seen in FIG. 1 (prior art) which represents an arteriotomy cannula commercially available from the DLP Division of Medtronic, Inc. This cannula comprises a body portion A having a lumen B extending therethrough with a bulb C provided at the distal end thereof and a female luer connector D provided at the proximal end thereof. The bulb C and rigid body A are integrally molded as a single unit whereas the luer connector D is molded independently of the body and secured thereto by conventional means.
The cannula seen in FIG. 1 (prior art) is ideally suited for use in an open heart surgical procedure because the surgeon can easily place the cannula in the operative position in view of the size of the chest wall opening.
A growing surgical trend is to move away from traditional open heart surgical procedures to more less traumatic minimally invasive cardiac surgical procedures. However, known surgical equipment such as the cannula 3seen in FIG. 1 is not well adapted for these minimally invasive surgical techniques. During most minimally invasive surgical techniques, the size of the surgical incision in the chest wall is dramatically reduced, thereby requiring maximum efficiency in the positioning and operation of the necessary surgical equipment. The structure of the known cannula may not be best suited for use in these procedures. An arteriotomy cannula used in a minimally invasive surgical procedure must have sufficient rigidity to be insertable into the coronary artery and yet have sufficient flexibility so that the cannula will not interfere with other surgical tools inserted through the relatively small chest wall opening.
The vessel cannula according to the invention overcomes the prior art by providing a cannula structure which has sufficient rigidity on the distal end thereof to permit insertion into the desired vessel and sufficient flexibility adjacent the proximal end thereof to permit easy movement and manipulation of the proximal end of the cannula after the distal end has been properly positioned in the vessel. Ideally, these problems are overcome by creating a cannula having properties such as rigidity which vary along the axial length thereof.
In a first aspect, the invention is directed to a cannula having two distinct body portions. The first body portion has a proximal end, a distal end, and a lumen formed therein extending between the proximal and distal ends. The first body portion has a prescribed rigidity or resistance to deflection identified as the first flexural rigidity. The second body portion similarly has a proximal end, a distal end, and a lumen formed therein extending between the ends. The proximal end of the second body portion is mounted to the distal end of the first body portion so that the lumens of the two portions are fluidly connected to one another. The second body portion similarly has a prescribed rigidity or resistance to deflection, different from the first, which is identified as the second flexural rigidity. The cannula is designed so that the second body portion is more rigid and less easily deformed or deflected than the first body portion. In the preferred embodiment, the first body portion has a flexural rigidity in the range of 3xc3x9710xe2x88x923 lbxc2x7in2 to 50 lbxc2x7in2, and the second body member has a rigidity in the range of 1xc3x9710xe2x88x924 to 4xc3x9710xe2x88x923 lbxc2x7in2.
A cannula having this structure is ideally suited for use in a minimally invasive surgical procedure whereby the size of the opening in the patient""s chest is dramatically smaller than the wound typically created for traditional open heart surgical procedures. With this structure, the distal end of the second body portion can be inserted into the coronary artery while the proximal end of the first body portion is positioned outside the patient""s body. Preferably, the second body portion is dimensioned so that when the distal end is properly mounted in the coronary artery, the proximal end of the more rigid second body portion does not extend significantly above the surface of the patient""s skin adjacent the chest wound. In addition, the first body portion preferably lays down across the patient""s chest, thereby avoiding potential interference with surgical tools and procedures.